Shill has primarily been used as an insult for the past 50 years in the way I’m defining it here. I don’t believe you’ve never heard it used to mean that.

one who acts as a decoy (as for a pitchman or gambler)

Literally on that same page.

a person who poses as a customer in order to decoy others into participating, as at a gambling house, auction, confidence game, etc.

https://www.dictionary.com/browse/shill

a person who publicizes or praises something or someone for reasons of self-interest, personal profit, or friendship or loyalty

https://www.dictionary.com/browse/shill

someone who helps another person to persuade people to buy something, especially by pretending to be a satisfied customer

https://dictionary.cambridge.org/us/dictionary/english/shill?q=shill

shill n informal, US (person planted to lure customers)

https://www.wordreference.com/es/translation.asp?tranword=shill

A shill, also called a plant or a stooge, is a person who publicly helps or gives credibility to a person or organization without disclosing that they have a close relationship with said person or organization, or have been paid to do so.

https://en.m.wikipedia.org/wiki/Shill

If someone starts off saying “this is a sponsores stream” then yes, that is correct. It’s illegal to not disclose when media is an advertisement in most of the world. I’m pretty sure it’s against the TOS of most streaming sites, too.

A shill doesn’t disclose that they’re being paid to promote a product. The secrecy is what makes them a shill

Yes, someone who promotes a product while hiding the fact that they’ve been paid to promote the product. Streamers generally say “this is a sponsored stream” to avoid lawsuits.

Plenty do, yeah. Though to the marketing team, all streamers are influencers

Sponsoring streams isn’t even close to the same thing as hiring shills