Cannot create new Messaging API Channel; 400 error in Web Browser Console Log

Pre condition, Condition to reproduce

1. Log in and enter Line Developers console (developers.line.biz/console)
2. Select a provider
3. Select "Create a new channel"
4. "Create a new channel" dialog box will popup, select "Messaging API"
5. Fill in all the details, and check to make sure that here are no red "X" icons indicating error below any of the text boxes or options
6. Make sure to check all the boxes regarding legal documents
7. Select the green "Create" button
8. "Create a Messaging API channel with the following details?" dialog box will pop up, select the green "OK" button

Issue/ Error Message details

After selecting the green "OK" button in the "Create a Messaging API channel with the following details?" dialog box, as described in step 8 above, the dialog box will be closed. After the "Create a Messaging API channel with the following details?" dialog box closed, nothing happens. It will show the same page as before, with all the details still filled in the previous steps. The page didn't refresh, and the page didn't change or moved forward to the next step. The green "Create" button described the the step 7 also no longer works, clicking it now won't do anything. To try this again and make the green "Create" button work you have to refresh the page, or go out and select "Create a new channel" again - which you will need to fill in all the details again. There are no dialog box that appears after this. The Messaging API channel also wasn't create, and there are no new Line Official Account created either.

I've tried many methods, which are described in the "Resolution Tried" section in this post. I've opened my web browser's Console in Developer tools (F12 key on keyboard), which shows a one lone red error in the console log,

POST https://developers.line.biz/api/v1/channel/queryAgreements?productType=BOT 400

There are no more error other than this one. And different times I tried and with different methods yield the same error as thos one. I've included the full expanded detail of that error copied from exported log of the Web Browser Developer Console in the following section "Accompanying respective source code"

Accompanying respective source code

trycatch.js:220 
        
        
       POST https://developers.line.biz/api/v1/channel/queryAgreements?productType=BOT 400
(anonymous) @ trycatch.js:220
(anonymous) @ instrument.js:266
(anonymous) @ xhr.js:160
t.exports @ xhr.js:11
t.exports @ dispatchRequest.js:59
Promise.then (async)
s.request @ Axios.js:51
r.forEach.s.<computed> @ Axios.js:71
(anonymous) @ bind.js:9
Ms @ channel.ts:169
queryAgreements @ NewChannel.vue?965e:288
confirmOaConsent @ NewChannel.vue?965e:309
await in confirmOaConsent (async)
submit @ NewChannel.vue?965e:363
await in submit (async)
ie @ vue.runtime.esm.js:1863
n @ vue.runtime.esm.js:2188
Qr.a._wrapper @ vue.runtime.esm.js:6961
i @ helpers.js:72

Resolution Tried

Here are some methods that I tried, all of which yield the same unsuccessful results; and the same 400 error when the console ine Developer Tools are available in the browser : • Different devices: 3 Windows PC and an Android phone (via Chrome browser) • Different web browsers: Google Chrome, Firefox, Vivaldi, and Chromium Microsoft Edge • Disabling browser extensions • Tried in Incognito/InPrivate/Private browsing mode • Tried "Guest Mode" in web browsers, which resets the browser condition to clean brand-new state (ie. no browser extensions, default settings) • Different networks (multiple home and work networks)

Reference information (Version / Platform/ environment)

Line Developers console (developers.line.biz/console) https://developers.line.biz/console/channel/new?type=messaging-api&provider=<REDACTED>