Stuck with one to many relation implementation in asp.net

I have an university assigment where I need to create a full-stack application with using ASP.net with 2 databases(SQlite).In addition, connected to a Blazor UI.
My problem is that everytime I try to assign my client to a job I get an error that I can't assign an existing id.

Here is my values:
Client:

1. Id(Generated by EF)
2. Name
3. Address
4. Email

Job:

1. Id(Generated by EF)
2. ClientID
3. License Plate
4. Manufacturing Year
5. Work Category
6. Description
7. Severity
8. Work stage

Here is my link to my repo:

https://github.com/gmark1337/NI-Mechanic

It might be a trivial error of my own, but I would be grateful if someone lends a hand for me!

Thank you for reply in advance!