A good mix of upper and lowercase characters and numbers has got to be Base64. A straight convert doesn’t give anything. Start with Atbash

Z2tlNDdtYWdpYzkyMmtv

Convert Base64 to Ascii

gke47magic922ko

Not to sure how to explain this one but there is a total of 152 bits. I first made groups of 8

21071211 17211707 17211211 17201211 17201806 21071720 21071721 21071712 17212107 21071707 17071712 17071721 21071211 17071712 17201720 17202107 17201120 21071120 17211707

Let’s group them by the passcode format

We are looking for a 9 letter keyword with repeating letters at the 6th and 9th position

Using the regex expression ^…..(.)..\1$ to search the keyword list, the only possible result is KNOWLEDGE

We can now build the index using the Ascii values and assuming that the numbers are grouped in 4

So far the index is

Which gives us

71 86 81 51 5? 75 78 79 87 76 69 68 71 69 55 57 5? 7? 86

Where missing values for 1120 & 1806. Using a bit of brute force the full index is

Which gives us the following string

71 86 81 51 53 75 78 79 87 76 69 68 71 69 55 57 54 74 86

Convert decimal to Ascii

GVQ35KNOWLEDGE796JV

This is clearly a phone cipher

jmbsesidatanitwsebu

jmb76data927bu