Yup, This smapi works your using it wrong! One stop solution to smapi not working.

[RakibRyan]

For 1.4.5.151 For those who could not make smapi mod the game or failed to sign it was because the apk & obb file you got was premodified from wherever you downloaded it from. I tried the same as you by downloading it from internet not realizing they already modified it. Then I bought & tried on the original version & it worked without a problem. Note the play store version has apk file size 87MB & some other site has 100-150MB. But if you were to get the original files then it will work / if you buy it on play store, mod & refund It'll still work. I imagine most of the versions on the internet are modified that includes earlier versions too.

[Also please buy the original if you can afford to]