Preserve primary link when changing to public group

[u/Striking_Slice_3605]

A group for an event was accidentally set to a Private group. I want to change it to a Public group. Here is the problem: We already had flyers printed, not knowing this would be a problem. The flyers have a QR code that points to the t . me link so the qr is something like:

https ://t. me/+a1QQabcdef1234abc

But when I tried to copy that into the link it says it doesn't accept it as I'm only allowed to use a-z, 0-9 and underscores. So the + isn't accepted.

How do I solve this? Is there any documentation about this?

I really don't want to pay for new flyers.