UIN Not accepting in GSTR 1

Dear experts,

We are basically electrical contractors, we have raised the GST invoice to CPWD (Government department). they are given UIN Number.

Now, we have to file the GSTR 1.

But in that UIN nor accepting in GST Portal.

The below mentioned message displaying.
(The GSTIN/UIN is invalid. pls enter a valid GSRIN/UIN).

Pls. solve this issue.