You might find helpful the existing discussion on the topic that you can find with the tag here, which I also added to this post.

Copying over my thoughts from a recent comment thread (mostly because of the links to existing resources): 

I think matching fundraisers tend to generally be dishonest by overstating the counterfactualness of a matching fund. See this old post for a lot of the standard arguments for that: https://forum.effectivealtruism.org/posts/a2gYyTnAP36TxqdQp/matching-donation-fundraisers-can-be-harmfully-dishonest 

My response made some general points that I wish were more widely understood:

• Pitching matching donations as leverage (e.g. "double your impact") misrepresents the situation by overassigning credit for funds raised.
• This sort of dishonesty isn't just bad for your soul, but can actually harm the larger world - not just by eroding trust, but by causing people to misallocate their charity budgets.
• "Best practices" for a charity tend to promote this kind of dishonesty, because they're precisely those practices that work no matter what your charity is doing.
• If your charity is impact-oriented - if you care about outcomes rather than institutional success - then you should be able to do substantially better than "best practices".

See also this Jeff Kauffman post: https://forum.effectivealtruism.org/posts/hQtayqi3r6bo3EPoh/the-counterfactual-validity-of-donation-matching 

Or this old GiveWell post: https://blog.givewell.org/2011/12/15/why-you-shouldnt-let-donation-matching-affect-your-giving/ 

at giveffektivt.dk we cover transaction costs of donating. Similar to donation matching, it's likely the money we spend on transactions would be donated anyways.

I think it's fine to do this, but i'm unsure where the line should be drawn. We find that many people who donate worry far too much about transaction and overhead costs. By alleviating one of those we make it much more attractive to donate (though I don't think we've A/B tested this actually).

But following this logic should we say that "5 dollars could save a life" if we thought this would increase total donations? Despite this sentence being literally true, it feels highly misleading and I would have mixed feelings about such a message. (In practice I don't think stating this would increase donations - if anything the opposite)

My own belief is that this type of messaging often brings its benefits in the short term, but incurs its costs in the long term, if a donor feels deceived and becomes less inclined to donate going forward.

This ultimately is the heuristic I go by. If someone were to read up on a claim after donating, would they feel deceived? If yes, then don't make the claim.

I don't personally think I would feel deceived about donor matching, so my intutition is that its fine, but maybe others feel different.