Hi,

[user@SIN-R1-1] > /ip dhcp-client pri
Columns: INTERFACE, USE-PEER-DNS, ADD-DEFAULT-ROUTE, STATUS, ADDRESS
# INTERFACE USE-PEER-DNS ADD-DEFAULT-ROUTE STATUS ADDRESS
0 v80-modem1 no no bound x.x.x.x/32

/ip dhcp-client disable numbers=v80-modem1 <-- it's ok

after that I want to return the setting back

[user@SIN-R1-1] > /ip dhcp-client enable numbers=v80-modem1 <-- the interface is empty, I enter it manually
no such item

[user@SIN-R1-1] > /ip dhcp-client pri
Flags: X - DISABLED, I - INVALID
Columns: INTERFACE, USE-PEER-DNS, ADD-DEFAULT-ROUTE
# INTERFACE USE-PEER-DNS ADD-DEFAULT-ROUTE
0 X v80-modem1 no no

As a result it doesn't work when I try to enable
[:parse "/ip dhcp-client $1 $InterfaceISP2"]

v80-modem1 - vlan interfaces
RB3011 ver 7.11.2

v80-modem1 is not a number, is it?
The number is at the start of the line (the # column) and is 0 in this case.

why, then
user@SIN-R1-1] > /interface/ethernet/disable numbers= <-- press TAB
ether... ether9 sfp1
and working
?

I expect it's a bug. Ask MikroTik support if you care that much.
An interface name is not a number. Deal with it.

It's a pity that this is a bug and not a new feature

(evl /ip/dhcp-client/disablenumbers=v80-modem1)

VS

(evl /ip/dhcp-client/disablenumbers=(evl (evl /ip/dhcp-client/findwhere=$interface;$add-default-route;$default-route-distance;$us
e-peer-dns;$use-peer-ntp;$dhcp-options;$script;$status;$address;$netmask;$gateway;$dhcp-server;$primary-dns;$secondary-dns;$prima
ry-ntp;$secondary-ntp;$caps-managers;$expires-after;$invalid;$dynamic;$disabled;$comment;$.id;$.nextid;$.dead;(= $interf (- $v80
$modem1));0)))

beyond any bug:
1) numbers should not be used on scripts (this is not the time to explain here, see the other dozens of posts about it in the forum)
2) don't forget the quotes for the strings, especially if there is a "-" in the name
3) dhcp-client do not have name, so you must search it by interface

So, the correct syntax is:
Learn how to script first, then talk about bugs.

(evl /ip/dhcp-client/disablenumbers=(evl (evl /ip/dhcp-client/findwhere=$interface;$add-default-route;$default-route-distance;$us
e-peer-dns;$use-peer-ntp;$dhcp-options;$script;$status;$address;$netmask;$gateway;$dhcp-server;$primary-dns;$secondary-dns;$prima
ry-ntp;$secondary-ntp;$caps-managers;$expires-after;$invalid;$dynamic;$disabled;$comment;$.id;$.nextid;$.dead;(= $interf (- $v80
$modem1));0)))

&&

/ip dhcp-client disable [find where interface="v80-modem1"]

Isn't this the same thing?
that's not what the question was about ...

that's not what the question was about ...

Ah... NOT?

Topic title: Can't enable dhcp-client