When You Face This(Invalid IMEI & NVRAM Issu, Then You will also Face Thus Problem-SIM Card Not Working, Unknown Based Version...etc...)
Like-
1. Invalid IMEI
2. NVRAM Issu
3. SIM Card Not Working
Fix
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Just Download this Files(booth) & Flash Your Own Custom Recovery
1. Download : IMEI Fix
2. Download : NVRAM FIX
Credits
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1. XDA(Unknown thread)
2. Our TEAM