@click4dylan this happens when you take a job in MP and don't finish it and go into SP or the other way around.
To get new jobs in MP it's easier to jump to a service station using F7 or fast travel to one of your garages.
To play in MP it's advised to own your own truck and garage.
If you want this right now and skip the work to your own truck you can use the beginners save found here
Switching from SP time to MP can make you very rich very fast if you hire truckers and trucks to work for you, so be careful if this would spoil your fun or use it to your advantage.