I’ve soldered lots of pewter and since it and the solder you use are
so close in melting temp, it’s really welding more than soldering.
The solder will melt into the metal and act as a filler in the
joint, it generally won’t flow between the two pieces and bond them
like with silver, gold etc.
Tix is a good, easily available, low temp, strong solder, it melts
at 275 degrees, most high tin pewter at @ 475 - 500 degrees so it’s
a narrow window you’re working with.
Use a mini torch or a torch with a very small and concentrated soft
flame. Unless it’s a small or very thin piece, you’ll have a tough
time using a soldering iron because of the mass involved, it
probably won’t get the a large enough area hot enough to get the
solder to flow.
Get some scrap if you can and practice, it is touchy and collapses
into a puddle quickly.