Main OID as .1.3.6.1.4.1.

The full OID of "TPDIN-Monitor-WEB3" is .1.3.6.1.4.1.45621.3
The full OID of "product" is .1.3.6.1.4.1.45621.3.1
The full OID of "monitor" is .1.3.6.1.4.1.45621.3.3
The full OID of "mppt" is .1.3.6.1.4.1.45621.3.10

This is from an SNMP walk:
Variable = .iso.org.dod.internet.private.enterprises.45621.3.1.1
model Value = TPDIN-Monitor-WEB3
Variable = .iso.org.dod.internet.private.enterprises.45621.3.1.2
firmwareVersion Value = 1.0.5
Variable = .iso.org.dod.internet.private.enterprises.45621.3.1.3
buildDate Value = 2021-06-10
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.1
relay1 Value = 1
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.2
relay2 Value = 1
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.3
relay3 Value = 0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.4
relay4 Value = 0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.5
v1 Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.6
v2 Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.7
v3 Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.8
v4 Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.9
i1 Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.10
i2 Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.11
i3 Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.12
i4 Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.13
t1 Value = 24.8C
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.14
t2 Value = 30.1C
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.15
v1int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.16
v2int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.17
v3int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.18
v4int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.19
i1int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.20
i2int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.21
i3int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.22
i4int Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.23
t1int Value = 24.8
Variable = .iso.org.dod.internet.private.enterprises.45621.3.3.24
t2int Value = 30.1
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.1
mpptmodel Value = TP-SC24-20N-MPPT
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.2
batv Value = 12.7V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.3
bati Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.4
btemp Value = 25.0C
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.5
itemp Value = 22.0C
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.6
loadv Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.7
loadi Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.8
pvv Value = 0.0V
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.9
pvi Value = 0.0A
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.10
loadstate Value = off
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.11
batvint Value = 12.7
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.12
batiint Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.13
btempint Value = 25.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.14
itempint Value = 22.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.15
loadvint Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.16
loadiint Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.17
pvvint Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.18
pviint Value = 0.0
Variable = .iso.org.dod.internet.private.enterprises.45621.3.10.19
load Value = 0