I would like to bet against a currency, I have USD. for example: how can I bet against the EUR?
Unfortunately when I try to SELL (short) EUR with my broker - I am not allowed to. Are there other ways I can accomplish this?
A margin account should allow short-selling of FXE.
Otherwise a long position can be bought in a 2x inverse ETF of EUO.
Also on the stock market, there is a dollar bull ETF of UUP.
Many currency traders use leveraged accounts of futures accounts or of retail forex accounts. Futures positions have contango or backwardation while forex positions adjust to the spot price and pay or charge rollover interest.
With a futures account, just sell a Euro contract. With retail forex, just sell the EUR/USD currency pair .
If you can't trade FX directly, you could consider buying puts/selling calls on FXE or trading the ETF directly.