@Yoyoyo238 

Is this a NEW router, never used before, or new to you?

What is the exact error you are getting?

What are you entering, not the actual data, but a userID that created and a P/W you did? I mean were you able to sign-in before and used the same credentials?

Have tried a FACTORY RESET?

I assume you'd followed the manual to do this, see https://static.tp-link.com/2018/201807/20180705/1910012437_AC500AC50_UG.pdf on Section 1.2.2?

The AC50 is not a Router, so you might be better served in the forum for it, https://community.tp-link.com/en/business/forum/1?page=1