Can my multi recipients still sign if my plan was downgraded?

Hello, 
I sent an envelope to a number of people last year on a paid plan. 
This plan ran out in the meantime. 

Now the 3 last remaining people tried to sign the document and all reported that the link they received is not working. 

The document is supposed to expire on March 18, 2026.

Is this related to the plan or could this be another error? 

Thank you.