投缘 and 合得来 are interchangeable and they both mean: hit if off, get along well, be on good terms, be friends, be friendly, be compatible, relate well to each other, etc.
Examples:
两人一见面就投缘。
The two of them hit it off as soon as they met.
他和约翰很投缘，并且很快两人便合伙做生意了。
He hit it off with John and soon the two of them run a business together.
过去他俩不大对头，现在却合得来了。
The two didn’t get along in the past, but now they hit it off well.
他和什么人都合得来。
He mixes well in any company.
看起来你和新邻居很合得来。
You sure seem to get along well with the new neighbors.