The seam sealing tape which the link points to is not the one you need for your bivibag. The clear tape is for 2 layer fabrics which have an exposed coating to which the glue can stick.
The bivibag is a 3 layer fabric which needs a high glue tape and longer heating time. It is important to get the glue hot enough and non viscous so it will flow down through the nylon scrim and penetrate to the membrane or coating underneath.
If you need some tape, pm me and I'll find some at work.
Hope that helps.
Graham