Quick answer: First check the browser context, number, code and whether you switched pages. GetTGAPI offers a mobile-friendly application page and Chinese-speaking support; device type alone does not determine success.
For help, contact support at gettgapi.com/en/help#contact. Already have an access code? Start at gettgapi.com/en/redeem.
Identify the failing stage
A mobile ERROR might mean a chat link fails to open, code verification fails, or Create returns no result. Record whether you see a number field, code field, app form or result.
Compare the same stage on desktop. Comparing a loading homepage with a submitted form response is not meaningful.
The page restarts after returning from Telegram
After checking a code in Telegram, return to the original tab. Clicking the chat link again can open another page rather than resume your application.
Use recent apps to return to the same browser. Avoid switching among embedded browsers, private windows and normal windows: they may not share site state.
Cookies can maintain site login, and clearing them may sign you out. Preserve your active environment while diagnosing. Chrome cookie guidance
Mobile input can differ
A keyboard or paste can add whitespace, newlines or full-width characters. Check the number, short name and code under their own rules rather than changing case everywhere.
Preserve the exact portal code. A short name can use simple English letters and digits. See code errors and app fields.
Desktop success does not prove mobile is prohibited
Browser, network, session, input and request time may all differ. Android or iPhone is not established as the cause by this comparison alone.
Check the official homepage in the phone's system browser and compare the same inputs. If Create was submitted on either device, read the result first; do not create simultaneously.
Reports of my.telegram.org says: ERROR after submission do not identify a particular phone platform as the cause. Original report
Using GetTGAPI on mobile
Ask support, obtain an access code and open the application page in one browser. After checking Telegram, return to that original tab.
Copy ID and Hash, check your saved copy, then delete the temporary result. Support explains the process; it does not need your code or access to your client.