This test purchase was cancelled because it was not acknowledged.

I integrated Revenuecat successfully in my Flutter App. When I make a test purchase from the app it gives the following terminal error: 

D//Purchases] - DEBUG(18782): 💰 kw_100_1y_1 - 
SkuDetails: {"productId":"kw_100_1y_1",etc...}
D/AudioTrack(18782): correcting timestamp time for pause, currentTimeNanos: 4563963963773 < limitNs: 4573594802304 < mStartNs: 4573694802304
D//Purchases] - DEBUG(18782): ℹ️ Found 0 unsynced attributes for App User ID: 3oTDvlvRsiuuuuuuuuuuuu
I/System.out(18782): (HTTPLog)-Static: isSBSettingEnabled false
I/System.out(18782): (HTTPLog)-Static: isSBSettingEnabled false
D/AudioTrack(18782): correcting timestamp time for pause, currentTimeNanos: 4563963963773 < limitNs: 4573594802304 < mStartNs: 4573694802304
W/AudioTrack(18782): getTimestamp() location moved from kernel to server
W/D/iPurchases] - DEBUG(18782): ℹ️ API request started: POST /receipts
D/rPurchases] - DEBUG(18782): ℹ️ API request completed with status: POST /receipts 503
E/rPurchases] - ERROR(18782): 🤖‼️ There was a problem with the store.
I/flutter (18782): PurchasesErrorCode.storeProblemError

I get a confirmation email that it was a successful subscription then after few minutes, I get another email from Google play stating the following: 

This test purchase was cancelled because it was not acknowledged. You should ensure that all purchases are acknowledged so that they are not subject to refunds. For more information, see https://developer.android.com/google/play/billing/integrate#process.