How project costs/expenditure can be captured between 2 different business units?

Dear community,

client has below challenges:

SY & TE are 2 different BUs and they want to share inventories in SY with TE, reason being both SY and TE are sharing some of the same equipment both for construction and fault handling at sites. So far this has not been an issue anyway as TE has continued to use the SY all cost occurred on TE tasks in SY has been invoiced from SY to TE.

But unfortunately, they now facing the challenge of sharing the inventories. As TE do not have the inventories it is not possible for their entrepreneurs to pick goods to the work orders.