Snapchat is hitting Instagram where it hurts.

Snapchat's parent company Snap Inc is offering free ad credits to advertisers who bought vertical video ads on Instagram in the last three months. 

The offer is also available to companies advertising on other platforms, but seems targeted at Instagram's advertisers. According to those with inside knowledge, the credits being offered are worth hundreds of dollars.

Ad revenue was the main factor in Snap's better than expected earnings for the final quarter of 2017. The earnings result made Q4 the company's most successful since its IPO. 

However, Snapchat needs to attract new advertisers to keep and increase its ad revenue. This is undoubtedly the main motivation behind this latest offering for advertisers. While the credits program is technically open for all advertisers buying video verticals, Instagram is the company's biggest rival in this space.

Look's like the company is finally taking the threat of Instagram seriously.