This probably won’t help, but I had to reload the yaml back onto the mini because I changed modems and hadn’t set a static ip. When I did, and then tried to use configuration-integration-esphome using the new ip, it gave me the “Can’t connect to ESP. Please make sure your YAML file contains an ‘api:’ line.” again. I tried several times before I gave up. It was giving temp and humidity readings in the log. I left it plugged in and 2 days later it appeared in integrations under esphome. It has been up for a few days and hopefully it won’t disappear.
I’m stuck in the same place.
Synology with ESPHome in docker.
When I try to add integration ESPHome in HA, it asks for host computer and there I write the IP to Synology.
Still: “Can’t connect to ESP. Please make sure your YAML file contains an ‘api:’ line.”
I have looked in numerus instructions but all left this part out.
What app are You referring to in Your first post?
I had the same problem (look here). I solved it by adding a passwort to the api section:
api:
password: "your-password-here"
What password is it?
Your password 
Have you ever solved the problem?
I had the same problem because I thought I had to enter the IP of my esphome (docker) instance with port 6052
But that was a fail. You have to enter the WLAN IP of the device. The port of the device will automatically be 6052 if you did not declare any other manually.
After connect you have to enter the api encryption key in home assistant that was installed on the device.
e.g. my device ir-receiver.yaml from esphome after i installed it on the d1_mini
esphome:
name: "ir-receiver"
platform: ESP8266
board: d1_mini
# Enable logging
logger:
level: VERBOSE
# Enable Home Assistant API
api:
encryption:
key: "2MeMPEGzET8U*******GCg1lFD1y+NkNI="
ota:
password: "bbe8d860***a6df8d2a5df0"
wifi:
ssid: !secret wifi_ssid
password: !secret wifi_password
manual_ip:
static_ip: 192.168.178.91
gateway: 192.168.178.1
subnet: 255.255.255.0
Its a little bit different thinkin of connecting if you are used to create a controller first…
It could be quite far-fetched that in the local network the communication between the devices must be allowed. I use a Fritzbox there is such a setting but have never tried it without. Therefore here only as additional info. If the device is pingable and no ports are blocked in the local firewall, this should work fine. Some esp devices also need a little longer until they are accessible.
I think many of this (fails) assumptions (and tries) presented in this thread wouldn’t be written here if users would just take a few minutes minutes to read the “Getting Started” guide: 
In detail: 
Connecting your device to Home Assistant
Once your configuration is installed on your ESP device and is online, it will be automatically discovered by Home Assistant and offered to set up on your integrations screen:
Alternatively, you can manually add the device on the Home Assistant Integrations page. Click on the “Add Integration” button (bottom right), search for esphome, and enter the host name, eg: “<NODE_NAME>.local” as the host. Use the same process to add multiple esphome devices.
Thank you for being so smart! 
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@ orange-assistant I read and installed using the “Getting Started” guides. ESP Home is installed and online however “HomeAssistant” detect the new device and when trying to add also get the silly message of
“Can’t connect to ESP. Please make sure your YAML file contains an ‘api:’ line.”
Have wasted hours on this and for now giving up as seems way too much hassle.and seems like many others have this issue with no answer on hand. So no, the “How To” provides zero instructions with dealing with this error.
What I really wonder - does your esphome YAML by accident or silliness doesn’t contain an api: line? 
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Yes, this is consistent issues , they keep updating and changing the interface and introducing new issies. The documentation is BS too.
Is it? For me it’s a constant non-issue 
Feel free to participate to make it better! It’s open source and everybody is invited to improve things like the documentation (specially users like you which having problems understanding the docs and therefor could make them better for everybody! 
)
There is even a guide how to contribute 
@orange-assistant: A stupid reply. How can one contribute to documents when one is learning . We come here asking for assistance. Your reply is totally unhelpful and puts one off asking for help.
Exactly these people who have a hard time learning know what additional information in the docs would have helped than achieve their goal faster. Users and devs which regularly work with esphome and the docs (and have already some knowledge) typically have no problems with the “BS” docs (@ForxPorx) likes to call them.
It’s just a point of view and it’s really necessary for the people who have problems understanding the documentation to improve them 
That’s okay (and that’s what the forum is there for indeed) - but sadly many people have problems even providing the minimum information necessery so others can actually help them. 
Also people (like you @myhass140) get offers/question to narrow down the problems but often don’t even bother to reply back 
Not much humans can do when an individual doesn’t want to get help 
Wow, clueless and rude or what! All my (few) questions posted are followed up in detail with whoever has “kindly” assisted me. I where possible also make note of “My Solutions & mistakes” so others can learn.
No response required as have unlinked myself from this thread as nothing to learn here.
Not that I’m aware of Maybe you see a different thread than the rest of us? Check January 19th 2023 of this thread 
followed by no reply of you (the person who seeking for help)
Maybe you thought
Mmm, do you see me asking a question anywhere there? All I did was agree about the “Getting Started” not being at all clear seeing as you were suggesting that we don’t read them.
You then went on to reply with what comes across as a “sneer” by writing:
I chose to move on as there wasn’t anything to learn here nor add. I certainly wasn’t going to reply to you then but am now. Perhaps try to be more helpful and leave off the “Laughing out loud at People” EMO’s. It’s not very becoming nor helpful.
The users tried to help you here just wanted to know (make sure) you have the api: line in your esphome yaml. As you didn’t post the yaml (How to ask a good question 
Format it properly) this is obviously the first doubt to clear with such a specific error message 
Which makes us wonder what you did. (How to ask a good question 
Describe what you changed)
Somewhat expect that for such a ‘clear’ error message there is no further details in the documentation.
In anyway what have probably been the most helpful (and probably the next question raised after confirming the api: line is in the yaml) would be posting your logs (How to ask a good question 
Share the logs)
That’s unfortunate but sadly you are not alone in not getting help. While most users are capable of asking “good questions” and even proactively provide yaml/logs (or when asked) there are also others that are struggling with the basics. Often these are the ones not receiving help simply because most people who want to support them have no crystal ball 
.
And while this posted picture mind be funny at first it is to often the case that users don’t read the docs or do a (1 minute) search before posting a question - which often leads to frustrations for the volunteers
This forum is not a helpdesk
The people here don’t work for Home Assistant, that’s an open source project. We are volunteering our free time to help others. Not all topics may get an answer, never mind one that helps you solve your problem.
Beside not everybody
The first post of @ForxPorx is a good example:
Not much of value…
Still wouldn’t make it more valuable so instead I pointed out that the “BS” documentation the user was ranting about is crowed sourced and that he got the power to change something (if he actually want’s too - which I indeed really much doubt based on his type of post).
It happens that users are not able to ask (good) question but still want help. So the volunteers here helping others in their free time also have skills “detecting” unasked questions. So for example if a user posts a error message often it indirectly implies a problem even giving no further information.
Anyway the fast majority in this community luckily acts in good faith and most users are also capable of getting help. 
Promoting How to help us help you - or How to ask a good question more so (specially new) users give it a 5 minute read is one of the few things the supporters can do with the hope improving the quality (and even quantity) of questions asked
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Pulling this old thread back to life as I just spend days down the rabbit hole after changes to my home network. Which changes broke it I cannot say for sure but my Rpi4 running HASS.IO is connected to the same vlan used for IoT devices as my access points.
My computer I use for my coding etc is on another vlan. I could ping my esphome device and flash it from my computer and home assistant would detect it but fail with the API message.
After literally days of looking at firewall configs and logs I decided to put my pc onto the same vlan and try again, this provided some interesting and strange results, I could still ping the esphome device, but I could no longer flash it over the network as I had previously.
so, for some reason my router was blocking some udp traffic between the devices.
Next I tried to ping and compile from computer attached to the saem access points as the esphome device, this worked.
So the issue was wired on the same vlan to wireless on the same vlan was blocking the handshake .
I made certain my router allowed traffic other then AP generated traffic on the VLAN it did.
I then found out about a hidden internal menu on the router that had additonal wireless settings to bypass the firewall rules for traffic between wired and wireless devices on the same vlan. After fixing this my issue was resolved.
So whilst ping may work you may have a similar traffic blocking setting in place that is not easily found.
My network setup is using all SonicPoint equipment, TZ350 firewall, SW14-24FPOE switch and a variety of SonicPoint APs, the article that finally helped me find the solution for my setup is here.
I hope this helps others out there.