tie-in vs linkup

tie-in and linkup both are nouns.

Word	Noun	Adjective	Verb	Adverb
tie-in	Yes	No	No	No
linkup	Yes	No	No	No

As nouns, tie-in and linkup are synonyms defined as:

Other synonyms of tie-in include link, tie.

tie-in (noun)	linkup (noun)
a fastener that serves to join or connect	a fastener that serves to join or connect