Microsoft Teams
Most shops have Teams because it came with the license; WorkCell will push the late job and the approval request into the channel anyway.
Communication
Teams usually arrives with the Microsoft license rather than by choice, which makes it the channel everyone is in and nobody checks closely. That is worth designing around. The notifications we plan to send are few and specific enough to be worth reading: this job is late, this lot failed inspection, this order needs your approval before purchasing can release it. Approvals come back from the message. Shops that bought into Microsoft already have the directory, so the people in the channel are the people in WorkCell, and the work is matching one to the other rather than inviting everybody twice.
Connect the systems you already use.
Tell us how Microsoft Teams fits your workflow and we will show you where it lands in WorkCell.