Check https://www.idmobile.co.uk/help-and-advice/credit-checks-explained FAQ, @Jessica Hepburn.

Thanks! But would you know why the first one was approved and the second one declined 

Okay @Jessica Hepburn, my guess is your second application was too close to the first time-wise, and the credit agencies thought a second iD loan too risky because very soon after first iD loan.

No business will say why an application failed, because this would allow bad actors to exploit the system and make fraudulent applications.

Hey there @Jessica Hepburn, welcome to Community!

As @andewhite has kindly advised, the above web-page on credit checks will advise general reasoning for this.

Sometimes, when ordering more than one contract at once, one may get declined due to the credit check etc. 

Thank you,

Tyler