Hi Michael
We have the following parameter to carry out availability check in sales order.
1- Plant has to be assigned to item level.
2- Requirement type should be assigned to requirement class.
3- Requirement class should be switched on for availability check.
4- Checking group should be assigned in material master.
5- Schedule line category should be switched on availability check.
Please check the above settings and do let me know.
Please focus specifically on Requirement type and class settings.
Regards
Neeraj