Form multi select issue

[Iyad Fa]

Hello everyone hope you all doing good. I am having a weird issue. If anyone is interested to help me i would be grateful.

I am using django 3.2.3 version and in my crispy form and one of my fields is as follows:

Every time i hit submit it gives me this error and i did the same thing a couple of months ago and it worked perfectly. I will share my code: 

forms.py:

Models.py:

Views.py:

Am i forgetting something? Before i used the same code and it worked perfectly

Thank you for your time in advance