Tower Ground Controller reported they cleared an aircraft to cross a runway at the same time that another aircraft was departing from the same runway.

Narrative

I was working Ground Control combined with Clearance Delivery; and my Local Control position was in training. I certified in Ground about 2 months prior.I had an Aircraft Y taxiing out of the FBO to RWY 19 via C holding short of RWY 19 [at] C. After scanning the field and RADAR; I believed the RWY 19 was clear to cross. I coordinated with LC (Local Control) for the crossing and was told to cross. While I was transmitting to Aircraft Y to cross; the trainer on LC got my attention and told me to hold; as Aircraft X was cleared for takeoff on RWY 19 and just rotated. In the same transmission (I never unkeyed); I told Aircraft Y to disregard and hold position. Aircraft Y subsequently keyed their mic and said they were crossing. I then immediately followed by instructing them to hold position and never was acknowledged by the pilot. Aircraft X flew over Aircraft Y at about 200AGL mid cross. Recommendation: I don't believe there is much a procedural change could do to help prevent this. I; as well as the Local Controller; should have a better scan before coordinating any crossing.