Software cause

[Commonder091]

My phone name is Samsung galaxy A51.

It's software is not updating, shows that your phone ...

[NasirRehman]

Cpid or patched phone?

[Commonder091]

I don't know. What's the matter but it's signal weakness also.

[Shahzx]

Matters alot.
Check on pta app if its cpid or patched.

[RANA_NAJAM]

Your device's operating system appears to be modified, such as being rooted or patched, which is the likely cause of this error. Please note that software support for the A51 model has concluded. Consequently, even if this error is resolved, no further updates will be provided for the device.