Gst 3b query

case 1
If Client A is un registered in gst and Client B is registered in gst

Client a issue invoice and client b cut 1 % tds on bill amount.

client a threshold limit crossed that 20 lack

but client b not accepting gst invoice from client a they just cut 1 %

is there any chance for notice to Client a

Case 2-
client a and b both are registered in gst but client b don't want gst invoice from client a
in that case what will happen

please reply for both case .