This term corresponds to definition 3.
There are multiple definitions - click on the translation that matches your context.
a game, food item or toy etc that is connected with a film or television programme etc
There is nothing new about the opening of a big blockbuster movie being accompanied by various marketing tie-ins.
when two or more companies try to work together to sell their products
Funky Rugs, the UK's leading online rug store, is pleased to announce a tie-in with The Natural Rug Store.
where two or more products must be bought together; a product that is sold this way
In tie-in sales of other subscriptions and devices used on the mobile phone network the consumer is protected by the tie-in sales provision in the Communications Market Act.